1. Field
The disclosure relates to a secondary battery, and more particularly, to a flexible secondary battery.
2. Description of the Related Art
With the development of electronics, not only markets for cellular phones, portable multimedia players (“PMP”s), and MPEG audio layer-3 (“MP3”) players, but also markets for other various portable electronic devices such as smartphones, smart pads, electronic book readers, flexible tablet computers, and portable medical devices attachable to the human body have grown.
The growth of markets for such portable electronic devices has increased demand for batteries suitable for operating such portable electronic devices. In addition, such portable electronic devices are increasingly required to be flexible in view of durability during transportation, storage, and impact, and thus the demand for flexible batteries has also increased.
If batteries having insufficient flexibility are bent, for example, stress may be concentrated on an internal interface of an electrode active material layer, an interface between an electrode active material layer and an inter-electrode separator, or an interface between an electrode active material layer and a collector, and thus stripping may occur at such interfaces, to affect the safety, performance and lifespans of the batteries.
If batteries of the related art are twisted or bent, the performance of the batteries may be lowered, or undesired reactions may occur in the batteries. Therefore, such batteries may not be effectively used for the flexible electronic device. Sheet-type batteries having small thicknesses for improving flexibility have been introduced. However, such sheet-type batteries typically have low energy capacity and thus have limited applications.